Because you sometimes want to filter, sort or project your data. Then you have to handle this in viewmodels or invent more and more features for the templating language. Then you want to refactor into components. So you need facilities for invoking subcomponents. Maybe you want something recursive to display tree-like data.

So you end up with a secondary full featured language usually with worse IDE support, worse error messages, more surprising issues, etc. You need to understand the scoping mecanisms and if things go wrong hope there is a debug tool available.

And in the end those templating languages do not prevent you from mixing UI responsibilities from the rest of your code.

If you want a reactive model you can have one. I personally prefer explicit messages like calling setState.

> Because you sometimes want to filter, sort or project your data.

The idea that this type of thing should be happening anywhere near the view rendering loop is the exact reason I've not had a great time picking up React codebases.

By the time you're rendering data into markup, the data should be in the exact state you need it. No further filtering or data mangling or sorting. That type of data manipulation should happen at the point of data change and then it shouldn't happen again until the data changes again.

The simplistic templating languages in Vue/Svelte/Alpine/whatever-comes-next force you to pull your data manipulation back to somewhere more appropriate, with Vue even throwing a warning if you try to filter within v-for construct.

Because React is JS, people are let loose to do wildly inefficient operations and do them over and over and over whenever _anything_ in that component changes.

I love vue’s concept of computeds. It makes me think back to knockoutjs when things felt like they “just worked” as long as you knew where the ES5 footguns were.

It’s nice to have a concept “ground truth” in data and props and then computeds that sort of tie it all together.

My feelings exactly, it makes for a satisfying separation of concerns, and if you understand what's going on under the hood it makes for cleaner templates and more obvious component code.

Yes, and those are available as well with MobX (in React), Svelte, etc.

You can do same/similar with React hooks, just not as clean or obvious.

You can 100% do these things in React, I don't believe React is a less able framework by any means. If anything it gives you a powerful toolbox and pulls down the guard rails.

I do, however, think that working with React changes your mental model somewhat, and when I'm working with React I catch myself doing a lot more data wrangling close or in the rendering loop than I would in any other modern framework. Certainly since class components have fallen out of favour, you're working with a function designed to be run hundreds of times, while Vue and Svelte both provide clear patterns to deal with data at the point of change, then separately deal with updating the display of that data as required.

It takes using something like MobX to really push a React codebase to a data-driven model and that means many inexperienced developers fall into the common pitfalls far more easily than if they're using an alternative framework imo.

Exactly. The whole paradigm of reactive data binding is that data dictates what the UI should render. Don't solve your data needs when rendering ffs.

> So you end up with a secondary full featured language usually with worse IDE support, worse error messages, more surprising issues, etc.

Gilad Bracha calls these "shadow worlds" https://gbracha.blogspot.com/2014/09/a-domain-of-shadows.htm...

Haven't used solidjs before, but I paid the doc section a quick visit and saw that it's basically <For each={foobar}> where foobar can be whatever javascript code you want. So you can certainly do filter/sort/project on your data before rendering.

You’d probably not want to project inside that loop though, but before it, in a reactive effect.

A react feature that I appreciate is that it is "just javascript". It's easier to learn how to loop or have conditionals in React because it uses native JS features. It makes it easier to understand, for me.

Having templating DSLs in other frameworks isn't a deal breaker, but it's a pro of React that I appreciate.

But I mean, it's not really. A hook invocation looks exactly like a javascript function invocation. Except it's subject to hook rules. Those don't come from javascript. Those are language rules that come from react. And even worse, the syntax for invoking a hook is exactly the same as the syntax for calling a function.

I've not used Svelte, but when I've used such DSLs the problem tends to be that they're not very flexible, and as soon as you step outside of the provided helpers you're stuck and you just can't do the thing.

Do you have an example you've run into where a DSL such as Svelte's or Vue's has actually stopped you from doing something? Would be genuinely interested to see it as I've never run into such a situation myself.

It's true, but the counterpoint is that DSLs make your life much easier in 90% of the cases (if not more).

Personally I've never found a problem I wasn't able to solve in Svelte.

> It does not make code any harder to understand or to write,

Well, what can you tell me about TypeScript type inference for this custom DSL?

I wouldn't call <For> in Solid a custom DSL anymore than any given React component. And Solid looks to have good TS support.

https://www.solidjs.com/docs/latest/api#%3Cfor%3E

Have you used Vue 3? There is fantastic TypeScript support in templates, including comprehensive intellisense for the templates in VS Code with the Volar extension. Surprisingly, _refreshingly,_ good.

> What is so wrong, exactly, with "reinventing a concept that's already in the language"?

Nothing, inherently. Just like there's nothing inherently wrong with having extremely clear and simple rules for how to use hooks, and lint rules to identify when you're not following those rules. Nothing inherently wrong with either, some people just have strong distaste for one or the other.